Crack resistant coating for masonry structures

ABSTRACT

Masonry structures are susceptible to cracking due to distortion caused by movement of their foundation, vibration, and/or drying out subsequent to the construction of the structure. Such cracking often occurs after the structure has been painted. This results in the crack being transmitted through the coating of paint. Upon repainting of the masonry structure new cracks often develop and are transmitted through the paint coating within a short period of time. 
     This invention discloses a crack resistant coating for masonry structures comprising: 
     (1) a crack absorbing layer which is contiguous to the masonry structure which contains beads which are essentially spherical and which are bound by a resin binder, and 
     (2) a conventional coating layer which is contiguous to and covers the crack absorbing layer.

This is a divisional of application Ser. No. 944,082, filed on Dec. 22,1986 (now issued as U.S. Pat. No. 4,804,693 which is acontinuation-in-part of application Ser. No. 771,746, filed on Sep. 3,1985 (now U.S. Pat. No. 4,634,724), which is a divisional of applicationSer. No. 645,989, filed on Aug. 31, 1984 (now issued as U.S. Pat. No.4,562,109).

BACKGROUND OF THE INVENTION

The cracking of masonry structures is a very well known phenomenon.Concrete walls, concrete block walls, stone walls and brick walls areall very susceptible to cracking. This cracking is sometimes due todistortion caused by movements in the foundation of the masonrystructure. In other cases, crack formation is caused by vibrations inthe masonry structure and/or drying out subsequent to the constructionof the structure. Such cracking can occur after various time periodsincluding shortly after the masonry structure is constructed to periodsmany years after the construction of the structure. Unfortunately, suchcracks are generally transmitted through layers of paint which coat suchmasonry structures.

Masonry structures are painted with exterior coatings of varyingthicknesses both to provide the masonry structure with a degree ofprotection and as a decoration. The propagation of cracks through thecoating destroys both the coatings aesthetic beauty and the protectionthat it provides to the masonry structure. Cracks which are transmittedthrough such an exterior coating layer are both unsightly and provide apoint at which moisture can penetrate into the masonry structure. Forexample, wind can drive rain into such cracks with the moisture beingfurther transmitted into the structure by capillary forces into theinterior of the structure causing dampness, degradation of the material,and a reduction of the thermal insulation efficiency of the masonrystructure. At the same time, an acceleration in the degradation of theexterior takes place due to moisture and its expansion during freezingwhich acts between the coating and substrate as well as opening thecrack in the masonry structure even wider.

Systems are known which are designed to fill or cover cracks which havealready formed, such as sealants and mastics. These materials have achewing gum-like consistency which will accommodate a certain degree ofcrack enlargement, but at the same time have limited adhesion. Flexiblecoating systems are partially effective, but do not offer a totallysatisfactory solution for cracking in masonry structures.

SUMMARY OF THE INVENTION

The present invention relates to a crack resistant coating for masonrystructures. This coating is comprised of a crack absorbing layer whichis applied directly onto the masonry structure with a final conventionalcoating layer being applied to it. The crack absorbing layer does notallow for cracks which develop in the masonry structure to betransmitted to the final (outside) coating layer. The final coatinglayer is essentially a conventional coating which is applied to thecrack absorbing layer and forms the outer surface of the crack resistantcoating.

This invention more specifically describes a crack resistant coating formasonry structures comprising:

(1) a crack absorbing layer which is contiguous to the masonry structurewhich contains beads which are essentially spherical and which are boundby a resin binder, and

(2) a conventional coating layer which is contiguous to and covers thecrack absorbing layer.

A process for coating a masonry structure with a crack resistant coatingis also described with this process comprising:

(1) applying a crack absorbing layer to the masonry structure whereinthe crack absorbing layer contains beads which are essentially sphericaland which are bound by a resin binder, and

(2) applying a conventional coating layer to the crack absorbing layer.

This invention further reveals a composition for application to masonrystructures as a crack absorbing layer comprising a plurality of beadswhich are essentially spherical in structure which are homogeneouslymixed throughout a resin binder solution having a viscosity of fromabout 0.5 to about 10 poise at 10,000 seconds⁻¹ and a Brookfieldviscosity of at least 600 poise at 10 rpm.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will become more apparent from the followingdetailed description and accompanying drawings, in which

FIG. 1 is a cross-sectional view of a masonry structure which has beencoated with the crack resistant coating of this invention.

As can be seen by referring to FIG. 1 the masonry structure 1 is coatedwith a crack resistant coating which is comprised of two layers. Theselayers are a crack absorbing layer 2 which is applied directly onto themasonry structure 1 so as to be adjacent and contiguous to it and aconventional coating layer 5 which is applied to the crack absorbinglayer 2 so as to be adjacent and contiguous to it. The crack absorbinglayer 2 is comprised of beads 3 which are essentially spherical andwhich are bound by a resin binder 4.

Essentially any type of masonry structure can be treated with the crackresistant coatings of this invention. For example, the crack resistantcoatings of this invention can be applied to concrete or cement walls,brick wall, stone walls, and the like.

The crack absorbing layer is applied to the masonry structure as acomposition which is comprised of the beads which are homogeneouslymixed throughout a resin binder solution having a viscosity of from 0.5to 10 poise at 10,000 seconds⁻¹ and a Brookfield viscosity of at least600 poise at 10 rpm (revolutions per minute). This composition has aconsistency that allows it to be troweled onto a vertical masonrystructure, such as a wall. It is important for this composition to havea consistency that is thick enough to keep it from running afterapplication to a vertical masonry structure. It is preferred for theresin binder solution to have a viscosity ranging from 2 to 6 poise at10,000 seconds⁻¹ and a Brookfield viscosity of about 750 poise at 10rpm.

Many materials are suitable for use as the resin binder in the crackabsorbing layer. However, it is important for the resin binder toexhibit sufficient flexibility to allow a degree of rolling actionbetween the beads in order to absorb cracks which form in the masonrstructure. It is also important for the resin binder to exhibitsufficient adhesive properties so as to hold the beads together as wellas holding the crack absorbing layer to the masonry structure.

A variety of polydiene resins exhibit the properties that are necessaryfor the binder resin. Such polydiene resins will normally also containone or more vinyl-substituted aromatic monomers. Polydiene resins ofthis type are prepared by polymerizing one or more diene monomers withone or more vinyl-substituted aromatic monomers. Suchdiene/vinyl-substituted aromatic resin copolymers will generally containfrom about 70 weight percent to about 90 weight percent of thevinyl-substituted aromatic monomer and from about 10 weight percent toabout 30 weight percent of the diene resin. Pliolite™ S-5 which is soldby The Goodyear Tire & Rubber Company is an example of such adiene/vinyl-substituted aromatic resin. Some representative examples ofsuch diene monomers include 1,3-butadiene, isoprene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-1,3-pentadiene, 1,3-hexadiene, 2-phenyl-1,3-butadiene,1,3-heptadiene, 1,3-octadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene and the like. Isoprene and 1,3-butadiene are themost commonly used diene monomers in the polydiene resins which are usedas resin binders in the practice of this invention. Styrene,α-methylstyrene, vinyl toluene, 3-methylstyrene, 4-methylstyrene,4-cyclohexylstyrene, para-chlorostyrene, 3-vinyl- methylstyrene,4-vinyl-methylstyrene, 1-vinylnapthalene, 2-vinylnapthalene, and4-para-tolylstyrene are some representative examples ofvinyl-substituted aromatic monomers that can be polymerized into theresin binders of this invention.

Copolymers of vinyl-substituted aromatic monomers and acrylates are alsouseful as resin binders in the practice of this invention. The mostcommon acrylates used in these copolymers are 2-ethylhexylacrylate,isobutyl methylacrylate, and methyl methacrylate. The monomer ratio ofvinyl-substituted aromatic monomers to acrylate monomers in thesecopolymers can vary greatly. However, in most cases, such copolymerswhich are used as resin binders will contain from 15 weight percent to60 weight percent acrylate monomer and from 40 weight percent to 85weight percent vinyl-substituted aromatic monomer. Such resins arecommercially available from a variety of sources and include Pliolit™AC-4 and Pliolite™ AC-80 which are sold by The Goodyear Tire & RubberCompany. Pure acrylic resins, for example polyisobutyl methacrylate orcombinations of other acrylic monomers would also provide suitablebinder resins.

In some cases it will be advantageous to use a plasticizer in the binderresin in order to attain the properties which are desired. Numerousplasticizers can be used for this purpose. Some commonly usedplasticizers include halogenated paraffins (particularly chlorinatedparaffins), butyl stearate, dibutyl maleate, dibutyl phthalate, dibutylsebacate, diethyl malonate, dimethyl phthalate, dioctyl adipate, dioctylphthalate, ethyl cinnamate, methyl oleate, tricresyl phosphate,trimethyl phosphate, tributyl phosphate and trioctyl adipate. Personsskilled in the art will be able to select the type and amount ofplasticizers needed in order to attain the requisite combination ofproperties needed in the binder resin.

The resin binder is dissolved in a suitable solvent in order for thebeads to be mixed throughout it for application to the masonrystructure. Persons skilled in the art will be able to easily select anappropriate solvent for the particular binder resin being used. Somesolvents which are commonly used for this purpose include white mineralspirits (containing pure aliphatic or aromatic solvents or blends ofboth), methylene chloride, ethylene chloride, trichloroethane,chlorobenzene, acetone, methyl ethyl ketone, methyl isobutyl ketone,methyl isoamyl ketone, diisobutyl ketone, ethyl acetate, propyl acetate,butyl acetate, isobutyl isobutyrate, benzene, toluene, xylene, ethylbenzene, cyclohexanone, and carbon tetrachloride. Water can also be usedin conjunction with an appropriate emulsifier as a medium in which thebinder resin can be dispersed. Such an aqueous resin binder dispersioncan be used as a medium through which the beads can be homogeneouslymixed for application to the masonry structure.

In some cases it will be necessary for the resin binder solution oraqueous resin binder dispersion to further contain a thickener in orderto attain a viscosity which is in the required range. These thickenerscan be either organic or mineral. For example, hydrogenated castor oil,clay, or hydroxy ethyl cellulose can be used as the thickener. Certainresin binders will not require the employment of any externalthickeners. For instance, in cases where Pliolite™ AC-4 is used as theresin binder no external thickeners are required in order to attain thenecessary Brookfield viscosity for the resin binder solution. Personsskilled in the art will be able to adjust the amount of thickener,plasticizer, and solvent in order to obtain the required viscosity forthe resin binder solution. For instance, if Pliolite™ AC-4 is selectedas the resin binder a suitable ratio of resin to plasticizer will bewithin the range of 4:1 to 1:4. A preferred ratio of resin binder toplasticizer for Pliolite™ AC-4 is about 1:1.

The beads which are mixed throughout the resin binder solution can besolid or cellular and generally have an average diameter ranging from0.5 mm (millimeter) to about 6 mm. In most cases such beads have anaverage diameter ranging from 0.7 mm to about 4 mm. Some representativeexamples of suitable beads include solid glass beads, cellular (blown)glass beads, and expanded polystyrene beads. A particular advantageoffered by cellular glass beads and expanded polystyrene beads is theirability to improve thermal insulation.

In some cases it will be desirable to allow the solvent in the resinbinder solution to evaporate allowing the crack absorbing layer to "setup" before applying the final coating layer. The final coating layer isessentially a conventional paint or coating which is applied to thecrack absorbing layer. Thus, the conventional coating layer is adjacentand contiguous to the crack absorbing layer. The crack absorbing layerwill protect the final coating layer (conventional coating layer) fromcracks which form in the masonry structure. The crack absorbing layerabsorbs cracks rather than transmitting them to the outer coating whichin this case is the conventional coating layer. The crack absorbinglayer can protect the final coating layer from cracks as large as 5 mmin width which form in the masonry structure. The degree of protectionprovided by the crack absorbing layer from cracking in the masonrystructure is somewhat dependent upon its thickness. Thicker crackabsorbing layers naturally provide a higher degree of protection for thefinal coating layer than do thinner crack absorbing layers. Normally thecrack absorbing layer will have a thickness ranging from about 0.3 toabout 3 centimeters. More commonly, the crack absorbing layer will havea thickness ranging from 1 to 2 centimeters.

This invention is illustrated by the following example which is merelyfor the purpose of illustration and is not to be regarded as limitingthe scope of the invention or manner in which it may be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

EXAMPLE 1

Two pieces of asbestos sheeting were placed together side to side. Thesepieces of asbestos sheeting were squares measuring 10 cm by 10 cm. Thus,when the two pieces of sheeting were placed together, a rectangularsurface measuring 10 cm by 20 cm was formed. This surface was thencoated with a resin binder solution which contained beads which wereessentially spherical to provide a crack absorbing layer. This coatingof the crack absorbing layer was about 1.2 cm thick.

The resin binder used was Pliolite ™ AC-4 which is sold by The GoodyearTire & Rubber Company. The solvent used for making the resin bindersolution was white mineral spirits which contained about 50% to 60%aromatics. The resin binder solution also contained a chlorinatedparaffin plasticizer. The total solids content of the resin bindersolution was 20% with it containing 15% binder resin and 5% plasticizer.The beads used in the crack absorbing layer were Expanver™ cellularglass beads having an average diameter of about 0.4 cm.

The crack absorbing layer was then coated with a conventional decorativethick coating which contained a white pigment. The coating was thenallowed to dry or "set-up". The two pieces of coated asbestos sheetingwere then pulled apart to a distance of 5 mm. Thus, the crack absorbinglayer was stretched to absorb a 5 mm crack. The outside coating did notcrack.

This experiment shows that this crack resistant coating will not crackeven when the masonry structure it is coating develops a 5 mm crack. Thecrack absorbing layer absorbed the 5 mm crack, and it was nottransmitted through the final coating layer.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the scope of the invention.

What is claimed is:
 1. A crack resistant coating for masonry structures subject to cracking comprising:(1) a crack absorbing layer which is contiguous to the masonry structure which contains beads which are essentially spherical, which have an average diameter within the range of 0.5 mm to about 6 mm, and which are bound by a resin binder, and (2) a conventional coating layer which is contiguous to and covers the crack absorbing layer wherein the resin binder exhibits sufficient flexibility to allow a degree of rolling action between the beads, thereby absorbing cracks forming in the masonry structure and preventing the transmission of the cracks to the conventional coating layer.
 2. A crack resistant coating as specified in claim 1 wherein said beads have a diameter of from about 0.7 mm to about 4 mm.
 3. A crack resistant coating as specified in claim 2 wherein said resin binder further comprises a plasticizer.
 4. A crack resistant coating as specified in claim 3 wherein said beads are cellular glass beads.
 5. A crack resistant coating as specified in claim 4 wherein said crack absorbing layer is about 0.3 to 3 centimeters thick.
 6. A crack resistant coating as specified in claim 5 wherein said crack absorbing layer is from 1 to 2 centimeters thick.
 7. A crack resistant coating as specified in claim 6 wherein said plasticizer is a chlorinated paraffin.
 8. A crack resistant coating as specified in claim 7 wherein said resin binder is a copolymer of one or more vinyl-substituted aromatic monomers and one or more acrylate monomers. 